Managing sensitive habitats adjacent to the Port Botany expansion

The Penrhyn Estuary Habitat Enhancement Project (PEHEP), implemented by the Port Authority of New South Wales (NSW) is one of the most ambitious estuarine habitat rehabilitation projects in NSW. To compensate for the port expansion works completed in 2011, which reclaimed part of Botany Bay and partially enclosed the adjacent Penrhyn Estuary, the PEHEP aimed to rehabilitate and expand Penrhyn Estuary's ecologically important intertidal flat, saltmarsh, shorebird and seagrass habitats. The Estuary is known as an important roosting and feeding area for migratory shorebirds. Rehabilitation involved a hybrid approach whereby some degraded habitat was restored while some other areas were created and/or expanded. Intertidal sand/mud flats and saltmarsh were expanded for shorebird feeding, islands were created for roosting and a lookout and bird hide constructed for the community. New seagrass habitat was created and directly affected Posidonia australis (a threatened seagrass) was transplanted to other areas in Botany Bay. A key challenge was to determine the appropriate levels (relative to tidal range) and features that would maximise the functionality of newly created habitats. Numerical modelling was used to develop a design engineered to maintain water quality by facilitating tidal flushing and mitigating contamination from groundwater and industrial/urban inputs under transient and ambient conditions. The project had maintenance built-in to avoid unwanted encroachment by mangroves, weeds, bird disturbance by predators, noise and light. Another challenge was ensuring the PEHEP had suitable means of determining its success or failure. Cardno and the Port Authority of NSW designed and implemented a long-term, ecological monitoring program from 2012 - 2017 to assess the success of the PEHEP. This included the development of targets against which key indicators such as shorebird abundance, seagrass and saltmarsh condition and water quality were assessed through quantitative field investigations. Results to date demonstrate that many of the key indicators have been met or show a positive trend, although the numbers of shorebirds have not yet reached target pre-construction levels. The monitoring program is currently under review to determine whether there is a need for new mitigation or ameliorative measures towards meeting PEHEP targets in the longer term. Overall, the PEHEP is considered a useful model for how ports can coexist with important natural habitats with the combined aid of engineering and ecological solutions.